Prospective prequalifiers include Germany's Bilfinger & Berger, France’s Bouygues, Japan’s Daiho Corporation, Germany’s Ed Zueblin, Brazil’s Odebrecht and South Korea’s Samsung Corporation.

The tunnel will run for 42 kilometres from an existing pumping station on Abu Dhabi island to the Mafraq wastewater plant, before heading towards the Al-Wathba wastewater treatment plant.

The tunnel is being tendered as three design-and-build contracts. One will be for a 4-metre diameter 16.2km-long tunnel from Abu Dhabi island onto the mainland. Another will be for a 15.6km tunnel with a diameter of 5 metres from the Musafah area to Mafraq.

The third involves the construction of a 10km tunnel with a diameter of 5.5 metres, between Mafraq and Al-Wathba.

Each contract requires the design and construction of the main tunnel, access shafts and short connecting tunnels. It also covers any additional work such as data acquisition, liaising with other agencies, seeking statutory approvals and relocating services and equipment.

The tunnel is a major part of Abu Dhabi's AED4bn Strategic Tunnel Enhancement Programme (Step), formerly known as the Strategic Investment Programme.

The project also includes developing one or two pumping stations along deep-tunnel sewer routes, a series of smaller sewers connecting existing sewerage systems to the deep tunnel sewer, and the removal of existing pumping stations.

The gravity tunnel and the sewers feeding into it will enable Abu Dhabi Sewerage Services Company (ADSSC) to eventually decommission several existing pumping stations, thereby reducing its operating and maintenance costs.

US-based CH2M Hill is the programme manager for Step and the entire programme is expected to take six years to complete.

ADSSC is the client (MEED 31:8:08).